For the purpose of monitoring information concerning the inside of the tire, including the air pressure and the temperature, a conventional practice has been to install an electronic device including various sensors in a tire air chamber, and thus to cause a receiver outside the tire to receive data from the electronic device by use of radio waves (see Japanese patent application Kokai publication No. 2002-324292, for example).
In the case of vehicles including trucks and buses in particular, radio waves attenuate to a large extent due to influence of structure of the tire while the radio waves pass the tire. For this reason, a receiving antenna is installed in each of the wheel houses. For the purpose of protecting an antenna circuit, the receiving antenna is installed on the motor vehicle so as to be in a state of being contained in a rigid resin case.
However, if the receiving antenna contained in the rigid resin case is arranged near the tire, the resin case may be damaged due to a stone flown or the like in some cases. In addition, in a case where the resin case is covered with snow due to the motor vehicle's drive on a snowed road, radio waves can not be received. When the snow is intended to be wiped off, it is likely that the rigid resin case may be damaged. Then, if the resin case is damaged, it is likely that the receiving antenna and the antenna circuit, which are contained in the damaged resin case, may be destroyed.